The subject invention relates to synthetic polymers containing a dispersed insecticide. More specifically, the present invention relates to a method of causing the migration of said insecticide to the surface of the synthetic polymer at a continuous and uniform rate sufficient to destroy pest insects by short term contact on said polymer surface. By adjustments of the migration rate, long term insecticide migration is possible. Thus, long term control of the target pest with improved economy and reduced environmental impact over other control methodologies, such as the use of area sprays and the like is possible.
Heretofore, it is known that pesticidal properties can be imparted to polymeric materials by incorporating a pest control agent in said polymer with various additives. U.S. Pat. No. 3,417,181 teaches that organotin pesticides can be dissolved in elastomeric polymers and caused to release through a diffusion-dissolution mechanism in water. Likewise, U.S. Pat. Nos. 3,590,119, 3,426,473, 3,851,053 and 3,639,583 extend the nature of the toxicant used and teach methods of formulation, but in all cases, activity is dependent upon the solubility of the given agent in the polymeric base and release occurring in an aqueous environment. U.S. Pat. No. 4,012,221 teaches that wherein a nonsoluble agent is incorporated in an elastomeric-type polymer, release can be afforded in a water environment if the amount so incorporated of said agent is sufficiently high and a water soluble coleachant is used to regulate the polymer/water interface. Plastic type materials and environments other than water are excluded from the above patents.
It is well known to the compounding art that agents which are not soluble within a polymeric matrix will not generally move at efficient rates through the matrix in that the propulsive force of solution pressure does not exist. Consequently, long term controlled release of nonsoluble agents heretofore has been thought impossible.
One method, now a recognized part of the pesticide polymeric formulation art, relies upon the use of a third phase material through which the pesticides is transmitted to the polymer surface. Specifically, this methodology relies upon the use of a polyvinyl chloride matrix to which is added one or more of several chemicals generically termed plasticizers and one or more pesticides. Since the plasticizing element is soluble to some extent within the polyvinyl chloride matrix, the molecules thereof will gradually flow towards the polymeric material and surface and usually removed from said surface by volatilization or mechanical washing, or other action of a nonchemical nature. If the given pesticide molecules are soluble or dispersable within said plasticizer, said pesticide molecules will migrate in the plasticizer flow and thus reach the surface. In such one well known application described in a number of patents such as U.S. Pat. Nos. 2,956,073, 3,116,201 and 3,318,769, a volatile insecticide is released for several months causing a vapor-induced toxicity to insects in the lethal zone surrounding the dispersing plastic commodity.
A plasticized polyvinyl chloride, prepared as a plastisol, containing a given amount of a toxic agent wherein the amount of said agent reaching the surface is controlled through the lamination of a plastic membrane on that surface is described in U.S. Pat. No. 3,705,938 and others. In this instance, contact poisons move slowly to the polymer dispenser surface controlled by additional means of the regulating laminated membrane, creating a toxic surface lethal, by contact, to insects moving across said surface. A similar technique is used in preparing bactericidal polymers as described in the above-listed U.S. Pat. Nos. 3,705,938 and 3,288,669.
U.S. Pat. No. 3,212,967 teaches that a plastic type polymer can be created which will release a pesticide if the pesticide moiety is chemically bonded to the polymeric backbone and cleavage of said appended moiety can occur.
In contrast, the present invention relates to the use of nonplasticized plastic type polymers that are not solutes for the given pesticidal agent, wherein the pesticidal agent is monolithically dispersed, (that is, generally, each agent molecule is completely enveloped by polymer molecules, as opposed to encapsulation wherein agent molecules are aggregated, and agent migration is through diffusion within said matrix, with the permeability being internally controlled and thus the migration rate is controlled without the use of a laminated surface membrane. Moreover, said polymer composition preferably contains an attractant-porosigen that similarly moves to the matrix/air interface, attracting the specific insect target to that surface with said insecticide eliciting chemotaxis in said insect.